deal with endian-ness in mach-o non-scattered relocs.

deal with endian-ness in mach-o non-scattered relocs.

BFD:

	* mach-o.c (bfd_mach_o_swap_in_non_scattered_reloc): New.
	(bfd_mach_o_canonicalize_one_reloc):  Swap non-scattered reloc
	bit-fields when target and host differ in endian-ness.  When
	PAIRs are non-scattered	find the 'symbol' from the preceding
	reloc.  Add FIXME re. reloc symbols on section boundaries.
	(bfd_mach_o_swap_out_non_scattered_reloc): New.
	(bfd_mach_o_write_relocs): Use bfd_mach_o_encode_non_scattered_reloc.

include/mach-o:

	* external.h: Add comments about relocations fields.  Add macros
	for non-scattered relocations.  Move scattered relocation macros to here.
	* reloc.h: Remove macros related to external representation of reloc fields.